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L0301P87 - Strategies For Control of Microbes
Microorganism Growth Control Importance of Control *bacteria are present almost everywhere *to prevent infectious diseases **in industries - particularly food *to use in and for research *to prevent hospital acquired infections *control can be achieved by: **preventing access bacteria **killing the bacteria **reducing numbers of bacteria **inhibiting growth of bacteria Factors Affecting Microbial Growth *temperature, moisture, osmotic pressure, pH, oxygen and nutrient availability Heath Care Setting Moist Organic Matter *supports bacterial growth **tissue, blood, body fluids, soiled linen and dressings **bacteria thrive and are protected Prevention of Disease Transmission Cleaning *must occur prior to any sterilising or disinfecting procedure *e.g. washing, soaking, hot water and soap or detergent *helps to control microbial growth Disinfection *removing or killing most viable organisms *physical (boiling water) *chemical (antiseptics) **antisepsis - removing microbes from skin Sterilisation *removing or killing all viable organisms **physical or chemical *destruction of all forms of microbial life Microbial Transmission - Risk Factors *equipment that may **penetrate skin or mucous membranes - highest risk - requires sterilisation **require specialised decontamination e.g: endoscopes, respiratory equipment **contact skin but not penetrate - lower risk - may disinfect or clean *human hands - disinfect between patients Sterilisation and Disinfection *heat - moist and dry *radiation - gamma and ultraviolet *filtration *chemical - liquid and gas Heat Sterilisation *highly efficient means of sterilisation *as long as the material to be sterilised is resistant to heat Moist Heat *much more efficient and effective *causes inactivation of proteins *aids penetration of heat into materials *killing of spores requires >100°C *boiling (100°C) only kills some organisms but not all **i.e. disinfection but not sterilisation Moist Heat with Pressure *kills bacterial cells, viruses, endospores **via denaturation of essential cellular proteins *machine: autoclave *increasing pressure, increases the temp at which water boils **121°C / 15 minutes **134°C / 3.5 minutes Dry Heat *inactivates cell components by oxidation *does not suit all types of materials **easily melts plastic objects *hot air oven **kills more slowly than moist heat **170°C / 1 hour, 160°C / 2 hours *incineration **destroys microbes ***infectious waste ***laboratory work (inoculating loops) Radiation *via ultraviolet, ionising, infrared, microwave Ultraviolet Radiation *kills bacteria by severe damage of DNA *is not penetrative **∴ used for disinfecting surfaces and air *requires longterm exposure to UV light *used in the disinfection of instruments, surfaces and water in hospitals *is damaging to human tissue as well as to many plastics Ionising (Gamma) Radiation *produces free radicals in the bacteria which breaks down their DNA *for heat sensitive materials and some foods **medical supplies eg. gloves, catheters, needles etc. Filtration *physically removes microorganisms from heat sensitive liquids or gases **IV bags, saline water for patients *membrane filter composed of polymers with different pore sizes (~ 0.22 μm) *vacuum pump attached to drive the filtering *used for materials that cannot be sterilised by other methods *used in the treatment for kidney failure **solution for surgical irrigation **peritoneal dialysis **intravenous therapy Chemical Sterilisation and Disinfection *used for equipment or materials that cannot withstand high temperature sterilisation *e.g.: endoscopes with fibre optics, catheters, large surfaces or fixed items *choice of a chemical for use depends upon: **number and type of microbes destroyed **purpose of treatment **type of item **interaction with other active chemicals **toxicity **cost Rules for Disinfection *article must be free of dirt, organic matter, grease, blood *solution must be at correct concentration *every part of article to be disinfected must come in contact with disinfecting solution *articles must be immersed for a sufficient period of time Disinfection *phenolics **environmental surfaces *iodine/iodophors **skin preparation for surgery *chlorine (sodium hypochlorite) **decontamination of blood spills *chlorhexidine **skin, handwash, surgical scrub *alcohol **skin decontamination - pre-injection **alcohol wipes - equipment *quaternary ammonium compounds **preservative in pharmaceutical preparations Sterilisation *traditional: **ethylene oxide gas, glutaraldehyde and formaldehyde (still used today) ***highly penetrative ***inactivate (alkylate) proteins and nucleic acid bases ***can kill a broad spectrum of microorganisms ***however also: toxic, flammable, irritant *recent: **vapour phase hydrogen peroxide (H2O2), peracetic acid (CH3CO3H), chlorine dioxide (ClO2), ozone (O3) Antiseptics *subset of the chemical disinfectants suitable for use on the skin or living tissues **alcohols, iodophors, chlorhexidine *antisepsis - to kill or remove harmful micro-organisms without damaging the tissue Sanitisation *thorough cleaning of an object or utensil to remove most microorganisms *note: this does not imply use of disinfectant Hospital Asepsis Asepsis *prevention of microbes from getting to a patient Medical Asepsis *practices and procedures to limit number of microorganisms in the healthcare setting Surgical Asepsis *keep all microorganisms away from tissues Aseptic Technique *protective measures and procedures designed to prevent spread of infection *e.g. gloves, gowns, masks, filtered air etc. Hospital Acquired Infections (Nosocomial) *breakdown in sterilisation and disinfection procedures *can occur via: **self-infection (patient) **cross-infection (staff, patient, visitors) **environmental (food, air, equipment, dust) *infections often caused by opportunistic pathogens, e.g.: **Staphylococcus aureus (Golden Staph) **Escherichia coli **Pseudomonas aeruginosa **Klebsiella pneumoniae Common Types Host Factors *underlying disease **e.g. due to diabetes, renal failure *invasive procedures *compromised natural defences **e.g. due to steroids, cytotoxic drugs *age **infants - immature immune system **elderly - declining immune system Prevention of Infection Exclude Source of Infection *monitor sterilisation/disinfection procedures *eliminate possible fomites e.g. ties *human sources are more difficult **identify staff who are carriers and prevent patient contact **implement work restrictions Prevent Transmission *control of airborne transmission *protective isolation *aseptic behaviour (hand-washing) **in both staff, patients and visitors Enhance Host Ability to Resist Infection *active and passive immunisation *prophylactic use of antibiotics **intended to prevent infection *care of invasive devices and attention to post-operative risks of infection Treatment of Microbial Infection Antimicrobial Agents *antimicrobial **any substance used for the treatment of infection **must be able to kill or inhibit the microorganisms responsible for the disease without causing damage to the host cells *e.g. antibiotic **low molecular weight compounds that kill or inhibit growth of bacteria **bactericidal ***kills the bacteria **bacteriostatic ***inhibits bacteria growth without killing **selective toxicity Range of Antimicrobial Activity *broad spectrum *narrow spectrum *bacteriostatic *bactericidal Sensitivity to Antibiotics Control of Bacterial Infections Targets *cell wall synthesis *cell membrane synthesis *protein synthesis **enzymes, transcription factors involved *folic acid metabolism Inhibition of Cell Wall Synthesis *most common target of antibiotic activity interfere with the synthesis of peptidoglycan Peptidoglycan Synthesis *is a polymer of: **N-acetyl glucosamine (NAG) **N-acetyl muramic acid (NAM) *NAM subunits joined by peptide cross-links **catalysed by carboxypeptidases and transpeptidases (PBPs) Examples of Cell Wall Synthesis Inhibitors *β-Lactam antibiotics **penicillins, cephalosporins, carbapenems **share β-lactam ring structure *Glycopeptides **vancomycin ***not active against Gram negatives *Polypeptides **bacitracin ***commonly used in the topical treatment of skins infections Example: Penicillin *produced by Penicillium chrysogenum *binds to PBPs and prevents cross-linking of NAM subunits *bactericidal *toxicity through allergy in some people *effective against: Gram positives *not effective against: **bacteria with no peptidoglycan in cell wall (Mycoplasma) **impenetrable cell walls (Mycobacteria) **bacteria not dividing Limitations of Antimicrobial Therapy *suppression of normal flora **promote opportunistic infections ***e.g. oral or vaginal thrush Candida albicans *adverse side effects **hypersensitivity - allergy **cytotoxicity - harmful to cells **nephrotoxicity - harmful to kidneys *emergence of resistance